1. Field of the Invention
The invention relates to a supervision circuit for a non-encoded binary bit stream conveyed through an elastic store having an input and an output, the rate at which the bit stream is applied to the input of the elastic store differing from the bit stream rate at the output of the elastic store, the latter comprising n locations, n bits of the binary bit stream always being written serially into the store by means of a write register and these n bits being read out serially by means of a read register, the register with the highest rate being stopped intermittently for one or more bit periods in order to equalize filling and emptying the elastic store. "Non-encoded" as used herein refers to absence of parity or other encoding for error detection.
2. Description of the Related Art
In PCM multiplex transmission systems an elastic store is comprised in the block converters, found at both the transmitting end and at the receiving end of the transmission system. At the transmitting end a bit stream is supplied to an elastic store which is preceded by a series arrangement formed by an equalizer, a regenerator and a decoder supplying a binary output signal. This binary output signal is applied to the input of the elastic store, and the binary output signal of the elastic store is applied to the multiplexer of the transmission system which multiplexes several such bit streams. At the receiving end, the binary signal originating from the demultiplexer corresponding to a given bit stream is applied to the input of an elastic store. The output signal of such elastic store is then applied to an encoder. Such a multiplex system is disclosed in Philips Telecommunications Review, vol. 38, no. 1, January 1980, pp. 11-22.
In the multiplex system described above the binary bit streams to be multiplexed, having slight mutual differences in frequency, are first brought to a common higher clock rate. This is realized by writing each one of these binary bit streams at its own clock rate into an elastic store and reading them from such store at a common higher clock rate. In order to prevent the elastic store from being emptied, the read clock is stopped periodically. Since there is a varying time relationship between the ingoing and outgoing binary bit streams of the elastic store, supervising the binary bit stream while being conveyed through the elastic store is not feasible by just comparing the binary input signal to the binary output signal. Besides, when passing through the elastic store, the binary bit stream is not encoded, and consequently it is not possible to make use of the redundancy provided in an encoded a bit stream, by detecting violations of the encoding rules.